Hi,
I'd like to be able to do replicateM, but over a vector instead of a list.
Right now I'm doing this:
import qualified Data.Vector.Generic as G
import qualified Data.Vector.Unboxed.Mutable as M
replicateM n action = do
mu - M.unsafeNew n
let go !i | i n = action = M.unsafeWrite mu i
Bulat wrote:
Hello Chad,
Tuesday, November 11, 2008, 10:23:09 PM, you wrote:
using unsafeFreeze. I'm getting stuck here, since the
IntMap library
is not so monad-friendly.
Data.Hashtable is
Well, I need mutable update for a while... after that, I prefer a pure
interface, which is
Thanks to all who responded about the benefits of using Cabal. After
trying out Bulat's Streams library, I thought I would download
ByteString (aka FPS) to compare the wc demos. To compile something using
Streams, I need to use a -i flag (thanks Bulat). When I followed the
README that comes with
-Original Message-
From: Henning Thielemann [mailto:[EMAIL PROTECTED]
Install locally after configuring this way:
./Setup.lhs configure --user --prefix=$HOME/yourlocalhaskelllibsdir
That seemed to do fine until it came to registering the package, which I
don't permission for.
AM
To: Scherrer, Chad
Cc: Henning Thielemann; haskell-cafe@haskell.org
Subject: Re: [Haskell-cafe] Trouble with Cabal
On 5/22/06, Scherrer, Chad [EMAIL PROTECTED] wrote:
-Original Message-
From: Henning Thielemann [mailto:[EMAIL PROTECTED]
Install locally after configuring
I was thinking about the dynamic behavior of par, and there's something
that's a little confusing to me. Am I right in understanding that (x
`par` y) evaluates to y, and may or may not evaluate x along the way?
I think it would be easier to reason about if we knew that x would be
evaluated,
Thanks, Bulat. Taking a look at Hal's FastIO library now...
Hal, it looks like your library could be helpful, especially if there is
a way to construct a FastIO.Handle from stdin. Can this be done, or do I
need to start with an actual file?
Thanks,
Chad
To read a file using a packed string, I need to use this function,
right?
hGetPS :: Handle - Int - IO PackedString
What's the Int? Do you have to specify the length in advance? I don't
know how packed strings are implemented, and I'm having trouble finding
much documentation.
I'm trying to
Daniel,
My knowledge of Clean is fairly limited (even more so than my knowledge
of Haskell), but no one seems to be responding to this, so I'll take a
crack at it. Here is why I've stuck with Haskell instead of Clean:
1. It runs well on Linux
2. The license is more open
3. There is a
PROTECTED]
Sent: Thursday, January 05, 2006 1:58 PM
To: Scherrer, Chad
Cc: [EMAIL PROTECTED]; haskell-cafe@haskell.org
Subject: Re: [Haskell-cafe] RE: Haskell vs. Clean
Hi
My knowledge of Clean is fairly limited
Mine too, but one of the biggest differences is that Clean
has uniqueness types
Several people on this list have said that the shootout favors imperative code.
Is this really the case? Why is it Clean seems to have no trouble (for the
incomplete set of benchmarks that are written in it)?
http://shootout.alioth.debian.org/clean.php
How difficult would it be to translate
--- Sebastian Sylvan [EMAIL PROTECTED]
wrote:
Some of the problems seem to be heavily geared towards an
imperative *implementation*, meaning that a Haskell version
is hardly idiomatic Haskell (and as such I , and I suspect
otehrs, really have no inclination to work on it).
This may be
Yes, good point. I suppose there's really no need to re-declare main once it's
been imported. Thanks!
-Original Message-
From: Remi Turk [mailto:[EMAIL PROTECTED]
Sent: Thu 12/29/2005 4:34 PM
To: Scherrer, Chad
Cc: S Koray Can; haskell-cafe@haskell.org
Subject: Re: [Haskell-cafe] RE
From: Daniel Carrera [EMAIL PROTECTED]
Hey,
The sqrt function is not doing what I want. This is what I want:
round sqrt(2)
---
Daniel,
A lot of Haskell folks like to avoid parentheses as much as possible, and
there's a really
From: Daniel Carrera [EMAIL PROTECTED]
Robert Dockins wrote:
-divides a b = (mod a b == 0)
+divides a b = (mod b a == 0)
Oh, thanks. My program assumed one way to define 'divides'
and the example assumed the other.
When I wrote it I was thinking of (divides a) being a
function that
-Original Message-
From: S Koray Can [mailto:[EMAIL PROTECTED]
Why not do this: name none of those modules Main.hs, and have an empty
module Main.hs with only import MainDeJour and main =
MainDeJour.main so you can just edit just that file.
Cheers,
Koray
Something about the way module names are specified in a file seems
really strange to me. When I first started learning Haskell (I had used
OCaml previously), I tried things like
module Main where
import A
import B
main = A.f B.f
module A where
f = ...
module B where
f =
Hi,
Can anyone suggest some references to learn how to program using GHC
with threads? I've read a little bit about STM, but it's still pretty
mysterious to me. Is this the best approach to take? I've never used
threads in any language, but monads are fairly comfortable for me.
Thanks!
Chad
On Tue, Dec 06, 2005 at 10:58:45PM +0300, Bulat Ziganshin wrote:
the third-priority problem is language itself. in particular, i hate
Haskell school of imperative manipulations:
x' - readIORef x
y' - readIORef y
writeIORef z (x'*y')
Here's a way to make some of this less messy:
raptor [EMAIL PROTECTED] writes,
]- that is the problem :), 'cause such functions should accept Char and
String, but return a Tuple of Strings, but it is recursive (so that it fetch
next,next,next char :)) i.e. it is own consumer and should return String
--this is wrong, just tring grab char
Hi,
I'm wondering about a syntactic sugar for comonads. These are still very
new to me, but it seems like their usage will become much more common
once manipulations are more convenient (I believe this was the case with
monads and arrows, correct?).
Here's an example for motivation. Consider
From: Cale Gibbard [mailto:[EMAIL PROTECTED]
See:
http://haskell.org/pipermail/haskell-cafe/2003-January/003794.html
The OI comonad as previously envisioned breaks referential
transparency. I/O just doesn't seem to be something which one
can easily do comonadically, since once
I've been reading some of the articles about comonads, and I thought the idea
of giving main the type OI () - () was pretty interesting. So I was wondering,
would it be possible to allow the type of main to be inferred? It seems like
IO ()
OI () - ()
OI () - IO ()
all make sense (at least I
Henning Thielemann [EMAIL PROTECTED] writes:
Since
(a . b) x
a $ b x
a (b x)
are equivalent, do you also want to reverse function and
argument in order to match argument order of . and $ ?
That is
x (b . a)
x b $ a
(x b) a
?
I'm sorry, I'm not sure I understand your
Henning Thielemann [EMAIL PROTECTED] writes:
I want to say, that the order of symbols for ($), (.) and
function application is consistent. This is a fine thing. I
think that shall not be distroyed by giving ($) and (.)
reversed argument order.
I see. I like the argument order also,
Udo Stenzel [EMAIL PROTECTED] writes:
The unix pipe is actually function composition. Its argument
(standard
input) isn't explicitly mentioned
Then it seems Unix must overload the | operator. I typically use it to
do things like
grep . *.hs | wc
So I think of the types as being
grep .
Albert Lai [EMAIL PROTECTED] writes:
I offer a simpler, more direct, and pre-existing correspondence
between a functional
programming construct and unix pipes:
Maybe my point wasn't clear. Of course this idea of comparing lazy
evaluation to Unix pipes is very old (long before July 2004, I'm
I'm still trying to settle on a feel for good programming style in
Haskell. One thing I've been making some use of lately is
(\|) = flip ($)
infixl 0 \|
Then expressions like
f4 $ f3 $ f2 $ f1 $ x
become
x \|
f1 \|
f2 \|
f3 \|
f4
I've seen something like this on haWiki using (#), but I
Surely not... sum is defined by Haskell 98 as:
sum = foldl (+) 0
and this is exactly what GHC provides. Furthermore we have
specialised strict versions for Int and Integer.
I'd been using ghci for testing along the way and getting terrible
results; does the specialization only
I was wondering... In my experience, it's worked much better to use
sum' = foldl' (+) 0
than the built-in sum function, which leaks memory like crazy for
large input lists. I'm guessing the built-in definition is
sum = foldr (+) 0
But as far as I know, (+) is always strict, so foldl' seems
You don't always want (+) to be strict. Consider working with
the ring of formal power series over, say, the integers. You
don't want (+) to force the evaluation of an infinite formal
summation which is passed to it, since that's an infinite
loop, so it will have to be non-strict,
The solution would be to bring 'sum' and 'product' into the Num class so
the most efficient version for each type can be used and the default is
no worse than the current non-class versions. (this is even pretty much
completly backwards compatable so could be considered for haskell 06)
I'd
Sorry to drag this thread out, but here's one more thing you might
try...
I was thinking, if we just wanted something like
intTable :: [Int] - [(Int, Int)]
we could just replace Map with IntMap in the previous solution:
intTable xs = IntMap.assocs $! foldl' f IntMap.empty xs
where f m x =
Hello, I need to calculate the frequency of each character in a
String. And if I can do this really well in C, I don't find a nice
(and
fast) answer in haskell. I tried several functions, listed below, and
even the fastest do a lot of unnecessary things :
A while back, I was trying to
For some reason the following code is producing an error
message from ghci that the the patterns are non-exhaustive.
Does anyone have any idea why that could be, given that the
patterns are, at least in my meaning, provably exhaustive?
You forgot to match against the empty list. Try
One of Mark Jones's articles suggests something like
class Plus a b c | a b - c where
(+) :: a - b - c
Would
instance (Plus a b c, Monad m) = Plus (m a) (m b) (m c) where
mx + my = do x - mx
y - my
return (x + y)
do what you're looking for?
Chad Scherrer
Hi,
I'm trying to use functionally dependent typeclasses to create an
overloaded (+=) function. A simplified example of a first bit of code
is...
class PlusEq a b c | a b - c where
(+=) :: a - b - c
instance (MArray a e m, Num e, Ix i) =
PlusEq (a i e) (a i e) (m ()) where
(+=) x y
When I compile with ghc -prof -auto-all, I end up with a .prof file that
starts out like this:
individualinherited
COST CENTRE MODULE no.entries %time %alloc %time %alloc
MAIN MAIN 1 0 0.00.0 100.0 100.0
Ah ha. That'll do.
Lesson: avoid hidden space leaks in monads.
Hmm, I'm still missing something. It seems a good lesson, but
practically speaking, it doesn't help me any more than saying write
efficient programs. What could I have looked for in the original code
to predict it may be leaky? Is
in general? Or
maybe some gains were made by switching from using StdGen with a specified seed
to using the OS-supplied random number generator?
-Chad
-Original Message-
From: Donald Bruce Stewart [mailto:[EMAIL PROTECTED]
Sent: Fri 8/19/2005 7:42 PM
To: Scherrer, Chad
Cc: haskell
Thanks! I was confused at first because ghci still runs into memory
problems, though no longer stack overflows. ghc runs it beautifully,
though.
-Chad
-Original Message-
From: Amanda Clare [mailto:[EMAIL PROTECTED]
Sent: Thursday, July 28, 2005 3:20 AM
To: Dean Herington
Cc: Scherrer
Title: stack overflow - nonobvious thunks?
I'm trying to write a function to build a table of values from a list. Here's my current attempt:
table :: (Ord a) = [a] - [(a,Int)]
table xs = Map.assocs $! foldl' f Map.empty xs
where
f m x = Map.insertWith (+) x 1 m
The ($!) and the
? The distinction between the two lists is still
vague to me.
-Chad
-Original Message-
From: Adrian Hey [mailto:[EMAIL PROTECTED]
Sent: Wednesday, July 27, 2005 12:04 AM
To: Scherrer, Chad
Cc: haskell@haskell.org
Subject: Re: [Haskell] combining IntMaps
Hello,
On Tuesday 26 Jul 2005 7:58 pm, Scherrer
for very large n like this.
-Chad
-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
Sent: Wednesday, July 27, 2005 11:02 AM
To: Scherrer, Chad
Cc: haskell@haskell.org
Subject: Re: [Haskell] stack overflow - nonobvious thunks?
Scherrer, Chad wrote:
f m x
functionality could not have otherwise been provided in
an efficient way without going into the guts of Data.Set?
Chad Scherrer
-Original Message-
From: Adrian Hey [mailto:[EMAIL PROTECTED]
Sent: Wednesday, July 20, 2005 10:57 PM
To: Scherrer, Chad; haskell@haskell.org
Subject: Re: [Haskell
Title: combining IntMaps
I'm using the (IntMap Int) type to implement functions (Int - Int), by treating non-keys as values that map to zero. I'd like to be able to add two of these pointwise, and delete the key from the resulting map when the sum of the values is zero. My specification is
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